Advancements in freezer/cooler door technology and a recent study from the Door and Access System Manufacturer’s Association (DASMA) now make it easier to choose which kind of door to use on a freezer/chilled room in a cold storage distribution center (DC).
Regardless of how official government policy is finally decided on the issue of climate change, industry has realized that going green saves money and businesses have embraced sustainability to bolster the bottom line. There are major retailers that have encouraged their supply chain partners to come on board as well.
In most DCs, the building’s interior consists of wide-open, un-walled spaces. In a cold storage DC the freezer and chilled rooms have to be their own separate environments in order to maintain product quality and prevent food spoilage. Being a low-margin business and any waste of course comes out of profits.
Nowhere is the cost of energy more keenly felt than in cold storage. Plant management at these facilities focuses on making cold air systems work as little as possible to optimize energy usage.
The Envelope, please
When it comes to saving energy, management talks about the “building envelope” and that term isn’t limited to merely the exterior. Facility managers work diligently to make sure every crack and gap in the walls of cold storage rooms are sealed to prevent the escape of precious cold air. Of course, these rooms have doorways and energy loss through them is a major issue.
Temperature differentials between the shipping/receiving docks and the cold storage rooms can be considerable—as much as minus 35 degrees Celsius and more. This difference is comparable to that between a standard building interior warmed to plus 5 degrees Celsius and the below-freezing weather outside.
Confining Cold Air or Letting in Traffic
Cold storage plant managers have been wrestling with the question of what kind of door works best for a cold storage room. After all, doors have two uses on this or any kind of facility – to allow access and to protect the activities taking place in the room in order to protect product quality. The two are seemingly in conflict.
When it comes to specifying cold storage doors, the plant manager faces two questions. Do I cover the opening with a door that is as thick as the wall itself to prevent heat transfer? On the other hand, do I use high-speed doors to prevent traffic back up into and out of cold storage?
In a growing number of facilities, the roof is being raised to 40 feet off the floor in order to reduce the roof area for minimizing energy loss. Down at the floor level there is a minimal wall perimeter, leading to less area for doorways, hence fewer doorways. Fewer doors can bring on traffic during busy periods, which for most 24/7 facilities means possible traffic jams – 24/7.
Some facilities seek out the fastest sliding-panel door they can get, but this style can attain speeds only half as fast as a true high-speed door, which can operate at nearly 125 inches per second. If the doorway is frequently accessed, these added seconds can accumulate to the equivalent of two days or more over the course of a year spent waiting for the door to open. Not a time good investment for your forklifts or their drivers.
Research Provides an Answer
So how should the management in a cold storage facility decide when it comes to door selection? After a two-year project featuring third-party lab testing, DASMA developed a method to demonstrate the efficiency of high-speed doors in building envelope energy calculations. The model for performance testing and evaluation was a prototypical, high-speed fabric door.
These findings follow research from 2012 on the relationship of high-speed doors to the provisions of American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings except Low-rise Residential Buildings, for non-residential buildings. Overall, DASMA noted that high-speed doors are the type of product that can significantly help achieve energy-saving goals.
The DASMA research revealed a new perspective in evaluating door energy efficiency and took into consideration common U-factor, air leakage, and motor horsepower values in a comparison of high-speed doors to conventionally operating insulated doors. The study showed that high-speed doors become more efficient when cycled 55 or more times per day, with that “crossover” point illustrated below.
Here’s how the study makes sense. The protection thicker doors provide against heat transfer is eventually negated if the doors are rarely closed. At that point, minimizing air infiltration becomes more of a factor for that doorway.
The kinds of high-speed doors the study had in mind have a roll-up design with a heavy-duty plastic fabric panel. For some measure of heat transfer resistance, there are models with double panels enclosing a layer of insulating foam.
Cold Air Stops at the Seal
Along with reducing air infiltration, high-speed roll-up doors offer a superior seal around the full door perimeter with side guides covering the vertical panel edges, a floor-hugging seal, and a brush seal along the top. Roll-up doors are better designed than solid-panel doors at sealing the door when closed.
The door’s operating life in an industrial/commercial setting pretty much involves getting out of the way of traffic that passes through the opening. Solid panel doors, being slower, are more likely to be hit by forklifts and other material handling vehicles. The damage that results can vary. Panels can be knocked out of alignment, forming gaps in the seal, have holes punched in them, or be totally knocked off the wall.
When that collision happens, the result is massive air infiltration and energy loss. If the door is totally disabled, the loss of one doorway in a busy cold storage facility can considerably cripple delivery schedules and wreak havoc with productivity.
If a high-speed roll-up door is hit and the panel knocked out of its guides, results are less severe. Most models have a self-repairing feature; the door is activated to roll up and then the panel rolls back into its guides. This design protects both the doorway and the facility’s ability to meet customer demands.
Sliding Doors Speeded Up
As to the speed problem with solid panel doors: Over the last few years a new sliding door design has come to market with a juiced-up performance of 2.5 meter per second — twice the speed of a standard sliding door — to handle traffic in busy DCs. The panels on these are used in minimizing both heat-transfer and infiltration. In addition, these doors can withstand accidental collisions from material handling vehicles, ensuring that the doorway is always available.
The question becomes, where would using a high-speed solid-panel door make sense versus a roll-up model?
Is the facility idle one shifts a day or one day a week?
During those periods, a solid-panel door would prevent significant heat transfer. If the operation is essentially 24/7, the door is rarely closed and the ultra-high-speed roll-up doors keep traffic moving and heat transfer is less of a factor.
How much wall area is available?
To facilitate sliding door operation, the wall area where sliding panels travel must be kept clear of racking and obstructions. For those facilities where management wants to use every inch of wall space, the roll-up style door, which is totally confined within the area of the doorway, will be the choice.
Does the facility have high ceilings?
To accommodate high-mast forklifts that reach product stored on racking up to 40’ above the floor typically requires 16’ doorways, making these openings more suitable for the lighter-weight roll-up door panels. Bear in mind that with the high ceiling scenario, the sliding door would be ruled out because wall space would likely be used for racking.
It’s All About Choice
The introduction of quick-operating sliding doors combined with DASMA research on suitability of high-speed doors means that doors can be specified according to the operation. Now management can make a door selection and be comfortable with it based on the needs of the operation.
Whatever the requirements of the facility, industrial door experts Gandhi Automation’s Pvt Ltd can provide advice and insight to tailor a door that delivers the performance and protection every doorway need.